Liebert Static Transfer Switch 2, Installation, Operation & Maintenance Manual

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14 Power and Control Wiring
Figure 3 Typical Static Transfer Switch One-Line Diagram
The input and output power wire size should be based on the upstream overcurrent protection
device, observing the NEC and local codes.
The molded case switches contained in the STS2 are typically non-automatic circuit breakers that
rely on the upstream and/or load overcurrent protection. Upstream overcurrent protection should
be rated equal to or less than the rating of the STS2 molded case switches.
The STS2 input and output power and ground and neutral bus bars accommodate a wide range of
wire sizes. The STS2 bus bars accommodates standard 2 hole lugs.
5.2 Input Junction Box Installation (Optional)
The input junction box option is available to simplify input connections to the STS2. Two input
junction boxes and the associated flexible 10 foot long (3 meter) input cables are provided with this
option.
This option is available only with bottom cable entrance, typically when the unit is located on a
raised floor.
If the input junction boxes will be used, they either can be shipped with the unit or shipped in
advance to be installed during the rough-in stage of construction.
Locate the junction boxes a maximum of 8 feet (2.4 meters) from the planned location of the Static
Switch.
Due to a lack of clearance for the cables below the unit, the cables are also shipped loose from the
unit for installation at the site. The input cables connect from the input junction boxes to the input
power bus bars inside the STS2.
The standard configuration for the input junction boxes and cables is for 3-wire-plus-ground feeds.
If the input neutral is required, special 4-wire-plus-ground input cables and junction boxes are
required. See
Figure 30 on page 48 for wiring details.
Table 3 Input/Output Conduit Plate Specifications
Rating Max. number and size
100-250A 6 — 3" conduit
400-600A 9 — 4" conduit
800-1000A 12 — 4" conduits
SOURCE 1 SOURCE 2
STS1 STS2
CB1 CB2
CB3 CB5 CB4
OUTPUT
K1
K2
K3 K2 K3 K1
SS1 SS2